Mechanical and chemical-mechanical planarizing processes (collectively “CMP”) are used in the manufacturing of microelectronic devices for forming a flat surface on semiconductor wafers, field emission displays and many other microelectronic-device substrate assemblies. CMP processes generally remove material from a substrate assembly to create a highly planar surface at a precise elevation in the layers of material on the substrate assembly.
FIG. 1 schematically illustrates an existing web-format planarizing machine 10 for planarizing a substrate assembly 12. The planarizing machine 10 has a support table 14 with a top panel 16 at a workstation where an operative portion (A) of a polishing pad 40 is positioned. The top panel 16 is generally a rigid plate to provide a flat, solid surface to support the operative section of the polishing pad 40 during planarization.
The planarizing machine 10 also has a plurality of rollers to guide, position and hold the polishing pad 40 over the top panel 16. The rollers include a supply roller 20, first and second idler rollers 21a and 21b, first and second guide rollers 22a and 22b, and a take-up roller 23. The supply roller 20 carries an unused or preoperative portion of the polishing pad 40, and the take-up roller 23 carries a used or post-operative portion of the polishing pad 40. Additionally, the first idler roller 21a and the first guide roller 22a stretch the polishing pad 40 over the top panel 16 to hold the polishing pad 40 stationary during operation. A drive motor (not shown) drives at least one of the supply roller 20 and the take-up roller 23 to sequentially advance the polishing pad 40 across the top panel 16. As such, clean preoperative sections of the polishing pad 40 may be quickly substituted for used sections to provide a consistent surface for planarizing the substrate assembly 12.
The web-format planarizing machine 10 also has a carrier assembly 30 that controls and protects the substrate assembly 12 during planarization. The carrier assembly 30 generally has a carrier head 31 with a plurality of vacuum holes 32 to pick up and release the substrate assembly 12 at appropriate stages of the planarizing cycle. A plurality of nozzles 41 attached to the carrier head 31 dispense a planarizing solution 42 onto a planarizing surface 43 of the polishing pad 40. The carrier assembly 30 also generally has a support gantry 34 carrying a drive assembly 35 that translates along the gantry 34. The drive assembly 35 generally has actuator 36, a drive shaft 37 coupled to the actuator 36, and an arm 38 projecting from the drive shaft 37. The arm 38 carries the carrier head 31 via another shaft 39 such that the drive assembly 35 orbits the carrier head 31 about an axis B—B offset from a center point C—C of the substrate assembly 12.
The polishing pad 40 and the planarizing solution 42 define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the substrate assembly 12. The web-format planarizing machine 10 typically uses a fixed-abrasive polishing pad having a plurality of abrasive particles fixedly bonded to a suspension material. The planarizing solutions 42 used with fixed-abrasive pads are generally “clean solutions” without abrasive particles because the abrasive particles in conventional abrasive CMP slurries may ruin the abrasive surface of fixed-abrasive pads. In other applications, the polishing pad 40 may be a nonabrasive pad composed of a polymeric material (e.g., polyurethane), a resin, or other suitable materials without abrasive particles. The planarizing solutions 42 used with nonabrasive polishing pads are typically “abrasive” CMP slurries with abrasive particles.
To planarize the substrate assembly 12 with the planarizing machine 10, the carrier assembly 30 presses the substrate assembly 12 against the planarizing surface 43 of the polishing pad 40 in the presence of the planarizing solution 42. The drive assembly 35 then orbits the carrier head 31 about the offset axis B—B to translate the substrate assembly 12 across the planarizing surface 43. As a result, the abrasive particles and/or the chemicals in the planarizing medium remove material from the surface of the substrate assembly 12.
CMP processes should consistently and accurately produce a uniformly planar surface on the substrate assembly 12 to enable precise fabrication of circuits and photo-patterns. For example, during the fabrication of transistors, contacts, interconnects and other components, many substrate assemblies develop large “step heights” that create a highly topographic surface across the substrate assembly 12. To enable the fabrication of integrated circuits with high densities of components, it is necessary to produce a highly planar substrate surface at several stages of processing the substrate assembly 12 because non-planar substrate surfaces significantly increase the difficulty of forming submicron features. For example, it is difficult to accurately focus photo-patterns to within tolerances of 0.1 μm on nonplanar substrate surfaces because submicron photolithographic equipment generally has a very limited depth of field. Thus, CMP processes are often used to transform a topographical substrate surface into a highly uniform, planar substrate surface.
In the competitive semiconductor industry, it is also highly desirable to have a high yield of operable devices after CMP processing by quickly producing a uniformly planar surface at a desired endpoint on a substrate assembly. For example, when a conductive layer on the substrate assembly 12 is under-planarized in the formation of contacts or interconnects, many of these components may not be electrically isolated from one another because undesirable portions of the conductive layer may remain on the substrate assembly 12. Additionally, when a substrate assembly 12 is over-planarized, components below the desired endpoint may be damaged or completely destroyed. Thus, to provide a high yield of operable microelectronic devices, CMP processing should quickly remove material until the desired endpoint is reached.
To accurately create highly planar substrate surfaces at the desired endpoint, the particle size distribution of planarizing slurries should be consistent from one planarizing cycle to another. One problem with CMP processing, however, is that the abrasive particles may be unstable in the slurry. For example, because many types of abrasive particles have a large affinity for one another, individual particles in a liquid solution may agglomerate into larger abrasive elements. The formation of such abrasive elements affects the consistency of the slurry because the extent that the particles agglomerate varies from one batch of slurry to another, or even within a single batch of slurry as it is delivered to the planarizing machine. Additionally, large abrasive elements may scratch the substrate assemblies and produce defects, or they may settle out of the solution. Thus, the agglomeration of abrasive particles is a serious problem for processing substrate assemblies with CMP processing.
One particularly promising CMP slurry being developed by Micron Technology, Inc. is a liquid solution having a plurality of first and second abrasive particles. The first and second abrasive particles are typically composed of the same material, such as ceria or silica treated ceria abrasive particles. The difference between the first and second abrasive particles is the size of the particles. This slurry accordingly has a “bi-modal” distribution of abrasive particles in which the first abrasive particles have particles sizes in a first size distribution about a first mode and the second abrasive particles have particle sizes in a second size distribution about a second mode. In contrast to “singlets ” slurries that have only one mode and a signal size distribution of abrasive particles about that mode, bi-modal slurries are expected to exhibit unusually good polishing rates and planarity on both topographical and planar substrate surfaces.
Although bi-modal slurries can produce good results, they may fail to achieve consistent results because the abrasive particles are highly unstable in the solution. The bi-modal slurries mixed by Micron Technology Inc. from components supplied by Rodel Corporation may even change from one planarizing cycle to the next, which greatly increases the difficulty in accurately planarizing substrate assemblies. To resolve the instability of these slurries, a point-of-use filtering may be performed at the planarizing machine of a single flow of a bi-modal slurry having both the first and second planarizing particles. Filtering the bi-modal slurry, however, may alter the bi-modal distribution of abrasive particles to the extent that the bi-modal slurry loses at least some of the advantages of using two different particle sizes. Therefore, there is a need for improved bi-modal slurry techniques in CMP processing to achieve the potential advantages of such slurries.